Continuous pulping apparatus



Oct. 30, 1962 J. P. RICH 3,061,007

commuous PULPING APPARATUS Filed Jan. 24, 1961 United States Patent Ofiice Patented Get. 30, 1962 3,061 007 CONTINUOUS PULiENG APPARATUS John P. Rich, Nashua, N.H., assignor to Improved Maehinery Inc, Nashua, N.H., a corporation of Maine Filed Jan. 24, 1961, Ser. No. 84,710 8 Claims. (Cl. 162-437) This invention relates to the continuous pulping of fibrous materials, such as wood chips, and more particularly to novel apparatus for washing such materials following chemical treatment thereof.

The pulping of wood ships or other fibrous material and the like and their subsequent washing has long been carried out by a succession of treatments which may be summarized as chemically treating the chips, usually under pressure and for a substantial period of time, discharging the treated chips as pulp and finally washing the pulp on cylindrical .drum washers. Invariably, more than one washing must be carried out, so that a number of cylindrical drum washers must be used; commonly three or four, utilizing countercurrent liquid filtrate flow for washing as shown and described in Patent No. 2,745,- 712.

According to the present invention, nevertheless, novel apparatus is provided whereby one or more of the drum washers of such a series may be eliminated without substantially reducing the overall degree of washing of the pulp by first carrying out a complete continuous pulping and washing in a single vessel, usually pressurized, followed by a series of cylindrical washers. This has been accomplished by the novel combination with an upfiow vessel, of a wash water inlet mounted at the upper end thereof as Well as means for controlling the liquid level within the vessel so that a countercurrent diffusion washing zone with a superposed drainage zone is provided above the wood chip treatment zone in said vessel. The vessel itself is of the type shown and described-in Patent No. 2,878,116, having mechanical means for advancing the solid particle component, the wood chips, upwardly through the vessel independently of the flow of liquid therein by maintaining a compacted mass of said solid particles extending throughout the effective length of the vessel and exerting lifting force directly only on solid particles located at the lower end of the vessel. The ability of the apparatus of the invention to advance a columnar mass of chips upwardly through the vessel by exerting force only at the bottom of the column is vital to the operation of the invention. In no other Way can the advance of chips in large diameter towers be closely controlled with relatively simple mechanisms, while leaving the effective length of the vessel entirely unobstructed for chip advance and for uniform circulation by treating liquids as is required.

The downfiow of the washing liquid through the washing zone has been found to be particularly important because of its highly eificient countercurrent washing effect, while the drainage of the Wood chips in the superposed drainage zone is equally important because of the efiicient removal of a large proportion of contaminated wash water thereby, as will be hereinafter more fully explained. Too, the inherent stability of such an upfiow system is maintained by the use of washing liquid at a temperature of about the same order as that of thetreating liquid at the top of the treating zone or otherwise to establish a stable density relationship and so avoid undesirable mixing. Thus, where a plurality of filters of the cylindrical type must be employed for washing, at least the first one of such filters may be replaced by the above described vessel with washing means therein by utilizing as Washing liquid the filtrate from the next succeeding washer of the series.

For the purpose of fully explaining preferred embodiments of the invention, reference is now made to the following specification, taken together with the accompanying diagrammatic drawing in side elevation of preferred apparatus according to the invention.

Referring to the drawing, the pressurized vessel 22 therein shown is generally similar to that shown in US. Patent No. 2,878,116, issued March 17, 1959, but further includes according to the present invention a washing liquid inlet, a liquid outlet strainer positioned Well below the inlet and the vessel discharge, and means for controlling the liquid level to a point well below the discharge level and above the strainer, thus providing three zones within the vessel, a pulping or cooking zone, a submerged countercurrent diffusion Washing zone thereabove and an uppermost drainage zone. In general, the apparatus ineludes a generally cylindrical upright elongated pressure vessel 22 of generally uniform cross-sectional area at least not decreasing in its upward direction having a bottom opening 18 connected to pump 16 and a top discharge mechanism connected to a suitable pulp storage tank. It is important that vessel 22, although of generally uniform cross-sectional area, have a slight taper to provide a gradually upward increasing cross-sectional area, a taper of about inch of diameter per foot of length, for example, being suitable. The advancing means includes a foraminous helical plate means 28 mounted for rotational and reciprocatory movement through a limited distance relatively to the length of the vessel within the reaction vessel 22 near the lower end thereof by means of a shaft 30 extending vertically through the bottom of said vessel generally axially thereof. More specifically, said foraminous helical plate means comprises a single turn helical plate 20 having therein a plurality of perforations sufficient in number to allow substantially free passage of liquid therethrough but of small enoughsize to prevent passage of the chips or other fibrous material. Furthermore, the step of such helical surface is closed by a fiat plate extending vertically between its upper and lower edges, and the peripheral edge thereof is positioned closely adjacent the inner walls of the reaction vessel 22 so that passage of chips into the bottom portion of said reaction vessel 22 may be prevented.

For feeding the pressurized mixture of chips and liquid to the upper surface of said plate, a tubular member 24 having its inner wall concentric with and spaced from shaft 30 is mounted on the lower surface of said helical plate extending downwardly therefrom, thus providing a central aperture between the upper and lower .radial edges of said helical plate. The lower end of shaft 30 extends into a hydraulic cylinder (not shown) mounted beneath the lower end of reaction vessel 22 and forms the piston thereof, said cylinder being connected to a suitable source of fluid pressure to raise said shaft with the helical plate to reciprocate said plate, the force of the vessel pressure against the area of the upper end of said shaft being great enough to rapidly lower theplate when the pressure in the cylinder is exhausted, the pressure vessel 22 in such circumstances acting as an accumulator to provide hhe necessary force at a rapid rate. Furthermore, the volume of liquid displaced by shaft 30 varies as the shaft reciprocates, causing the entire volume of liquid in vessel 22 to reciprocate over a limited distance.

The top discharge mechanism comprises scraper 26 located near the topof the vessel adapted to remove digested wood chips therefrom and so define the upper end of the mass of chips within vessel 22, as well as to define the upper end of the chip drainage zone. Scraper 26 moves the chips through housing 28, and discharges the chips to a vertical chamber 31. In thebottom zone of this chamber an upward facing, bladed agitator 48 is rotatably mounted and oper-ativelyconnected with a driving means 42. A chamber bottom surface 44 generally conforms with the path of the lower edge of the rotatable blades, to define the lower extremity of the bottom zone. At least one orifice 46 is positioned in the bottom zone of the chamber in the bottom surface 44 below the path of the bladed agitator 40 so that rotation of the bladed agitator causes each blade to wipe by the inlet to the orifice, preventing clogging. A gate valve assembly 48 is positioned in the orifice 46 for adjusting and closing its aperture, and, if desired, means may be provided for diluting pulp in the bottom zone in which agitator 40 operates. Such agitator and associated structure being fully shown and described in US. patent application Serial No. 805,503, filed April 10, 1959, need not herein be further described.

From the gate valve 48 the cooked and partially washed wood chips are discharged to atmospheric pressure for storage by means of a cyclone device mounted on a suitable 'pulp storage tank 52 having discharge means. Such apparatus is well known in the art, the cyclone device having a tangentially directed inlet opening into a cylindrical compartment which operates to reduce the velocity of the pulp emerging from valve 48 and to separate it from the steam with which it is entrained, which pulp then drops into a pulp storage tank having suitable dilution and discharge means such as is shown in Patent No. 2,745,274, for example.

From the pulp storage tank 52, the pulp is passed by means of a suitable pump 53, to the first washer, generally designated 54, of a series thereof, herein shown as washers 54 and 56 although more may be employed depending upon the degree of washing desired. Such washers and their interconnections may be, for example, such as is shown in Patent No. 2,745,274, wherein countercurrent washing is carried out by utilizing the filtrate from a succeeding washer as the washing liquid for a preceding washer.

According to the present invention, in addition to the access opening 18, a fluid access opening 19 may be located below the chip lifter plate through which liquid may be passed. It is essential, however, that a strainer 60 be provided spaced downwardly from the top of the vessel below the discharge opening 28 of the vessel for removal of liquid therefrom and to define the top of the pulping or cooking zone and the bottom of the submerged washing zone thereabove. Such strainer may be provided with a valve 61 controlled as hereafter described. A liquid level sensing device 62 may be suitably located to sense and establish as hereinafter set forth a liquid level above the strainer 60 and below the discharge opening 28. In addition, a series of wash liquid inlet openings 64 peripherally spaced in a horizontal plane around the vessel generally midway between the strainer 60 and discharge opening 28 are provided, preferably adjacent the top of the submerged washing zone and bottom of the drainage zone defined by the level sensing device 62. If desired, a wash liquid shower distribution pipe 65 is provided above scraper 26.

Three zones are thus defined within vessel 22: a lower pulping or cooking zone below the strainer 6%; an intermediate submerged washing zone above it; and an uppermost drainage zone. Means, such as a pump 66, are provided for feeding a supply of sufiiciently pressurized wash liquid to openings 64 or to shower 6S, and a heat exchanger 68 is provided for heating such liquid as may be required. With this novel arrangement the treated chips, as they are moved above strainer 60' will be subjected to a countercurrent -flow of heated wash liquid throughout the submerged washing zone between said strainer and the liquid level on vessel 22 defined by sensor. After moving above such level, they will be drained of the washing liquid and at the same time may be subjected to a flow of washing liquid from shower 65 for further washing. The liquid level may be controlled, for example, by adjusting strainer valve 61 in accordance with sensed level changes of device 62, although other level control means could also be employed.

if the washing of the treated chips within the pressurized vessel is to be followed by further washing in one or more cylindrical drum washers, then it is desirable that countercurrent washing be utilized throughout the system. Thus, if two washers be used as is shown in the drawing, they may be of a type with interconnections such as is shown and described in Patent No. 2,745,712. However, with the structure of the present invention arranged to precede such a series of washers, the washing liquid supplied to the wash liquid inlets of vessel 22 is taken from the filtrate of the next succeeding filter 54, the countercurrent flow of washing liquid through the series of filters 54, 56 being continued by the countercurrent flow of liquid through the washing zone within the reaction vessel.

It should be noted, however, that for successful operation of an upflow reaction vessel of the type described, wherein a countercurrent washing zone is superimposed above a cooking zone, it is necessary that the density of the liquid introduced into the upper zone be less than that of the liquid below in order to keep the zones stable. Otherwise the liquid in the upper zone will move downward by convection and cause mixing with the liquid below, reducing the efiiciency of the Washing. This difference in density of the liquids may be achieved according to the invention by controlling two factors, concentration and temperature. More specifically, because the flow of washing liquid in the system is countercurrent through washers 56 and 54 and then through the washing zone of vessel 22, the concentration of dissolved organic solids in the liquid is greatest just below strainer 60 and less at inlets '64 and thus producing the desired decrease in density throughout the washing zone. In addition, the temperature of the wash liquid leaving washer 54 is raised by means of heat exchanger 68 to approximately that of the cooking liquid, further decreasing the density of the wash liquid. It is convenient to heat the wash liquid as it passes through heat exchanger 68 by using the hot liquor from valve 61, thus eliminating the necessity of supplying steam at this point. The combined effects of concentration and temperature reduce the density of the wash liquid well below that of the cooking liquid even if the wash liquid temperature is somewhat less. Thus, there will be little mixing so that the submerged washing zone will be highly effective.

Thus it will be seen that the invention provides novel countercurrent pulp treatment and washing apparatus. Various modifications of the invention within the spirit thereof and the scope of the appended claims will be apparent to those skilled in the art.

What is claimed is:

1. Apparatus for the continuous pulping and washing of wood chips in a generally upright elongated reaction vessel by feeding substantially continuously said Wood chips and a pulping liquid into said reaction vessel adjacent the lower entrance end thereof to maintain a compacted mass of said wood chips within an elongated pulping zone in the central portion thereof, and a submerged washing zone followed by a drainage zone in the upper end portions thereof, advancing the wood chips upwardly through said zones at a rate substantially independent of the movement of treating liquid in said vessel, meanwhile treating the same by a pulping liquid, then by a washing liquid and finally draining said wood chips and substantially continuously discharging said pulped, washed and drained wood chips from said upper end of said vessel, said apparatus comprising wood chip lifting means mounted adjacent the entrance end of said vessel to exert lifting force directly only on wood chips located at the entrance end of said vessel progressively to compact said wood chips and to advance the mass of said wood chips progressively upwardly through said zones while permitting free movement of liquid through said mass, wood chip discharge means adjacent the upper end of said vessel effective to maintain a predetermined level of the top of said mass of wood chips below the top of said vessel, strainer means in said vessel spaced a substantial distance below said wood chip discharge means for removal of treating liquid from said vessel, liquid level control means for said vessel effective to sense and control the upper level of liquid in said vessel to a predetermined position a substantial distance above said strainer means and below the level of the top of said mass of wood chips, and washing liquid inlet means in said vessel located a substantial distance above said strainer mean for feeding washing liquid downwardly through a submerged washing zone between said upper level of liquid and said strainer means, the zone between the upper level of said liquid and the top of said mass of wood chips operating as a drainage zone for drainage of liquid from said chips before their discharge.

2. Apparatus as claimed in claim 1 wherein said washing liquid inlet means is located above said discharge means.

3. Apparatus as claimed in claim 1 wherein said washing liquid inlet means is located below said discharge means.

4. Apparatus as claimed in claim 1, further including means for controlling the density of said washing liquid to a value generally less than that of said pulping liquid at the top of said pulping zone preventing substantial mixing of said pulping liquid and said downwardly flowing washing liquid being discharged through said strainer means.

5. Apparatus as claimed in claim 4, further including means for feeding pulping liquid upwardly through said vessel for discharge through said strainer means with said washing liquid.

6. Apparatus for the continuous cooking and washing of wood chips in a generally upright elongated reaction vessel followed by one or more cylindrical drum washers by feeding substantially continuously said wood chips and a cooking liquid into said reaction vessel adjacent the lower entrance end thereof to maintain a compacted mass of said wood chips within an elongated cooking Zone in the central portion thereof and a submerged washing zone followed by a drainage zone in the opposite upper end portions thereof, advancing the wood chips upwardly through said zones at a rate substantially independent of the movement of treating liquid in said vessel, meanwhile treating the same, by a cooking liquid, then by a washing liquid and finally draining said wood chips, substantially continuously discharging said cooked, washed and drained wood chips from said opposite upper end of said vessel and then washing said treated wood chips as pulp on said cylindrical drum washers, utilizing the filtrate of the first drum washer after pressurizing to wash said wood chips in said vessel, said apparatus comprising wood chip lifting means mounted adjacent the entrance end of said vessel to exert lifting force directly only on wood chips located at the entrance end of said zones to progressively compact said wood chips and to advance the mass of said wood chips progressively upwardly through said zones while permitting free movement of liquid through said mass, wood chip discharge means adjacent the upper end of said vessel effective to maintain a predetermined level of the top of said mass of wood chips below the top of said vessel, strainer means in said vessel spaced a subwood chips, washing liquid inlet means in said vessel located a substantial distance above said strainer means and below said discharge means establishing the upper level of the top of said mass of wood chips, for feeding washing liquid downwardly through a submerged washing zone between said upper level of liquid and said strainer means, the zone between the upper level of said liquid and the top of said mass of wood chips operating as a drainage zone free of treating liquid for drainage of liquid from said chips before their discharge, a series of horizontal foraminous cylindrical drum washers of the type wherein washing liquid is sucked inwardly through the cylinder wall, means for separately collecting the filtrate from each washer, means for returning from the first washer at least a portion of the filtrate to the Washing liquid inlet means in said vessel, and means for returning from each succeeding filter at least a portion of the filtrate to the preceding filter.

7. Apparatus as claimed in claim 6, further including means for heating said filtrate from the first washer to a temperature of the order of that of the cooking liquid in said vessel at a point adjacent said strainer.

8. Apparatus for the continuous cooking and washing of wood chips in a generally upright elongated reaction vessel followed by one or more cylindrical drum washers by feeding substantially continuously said wood chips and a cooking liquid into said reaction vessel adjacent the lower entrance end thereof to maintain a compacted mass of said wood chips within an elongated cooking zone in the central portion thereof and a submerged washing zone in the opposite upper end portion thereof, advancing the wood chips upwardly through said zones at a rate substantially independent of the movement of treating liquid in said vessel, meanwhile treating the same by a cooking liquid and then by a washing liquid, substantially continuously discharging said cooked and washed wood chips from said opposite upper end of said vessel and then washing said treated wood chips as pulp on said cylindrical drum washers, utilizing the filtrate of the first drum washer to wash said wood chips in said vessel, said apparatus comprising wood chip lifting means mounted adjacent the entrance end of said vessel to exert lifting force directly only on wood chips located at the entrance end of said zones to progressively compact said wood chips and to advance the mass of said wood chips progressively upwardly through said zones while permitting free movement of liquid through said mass, wood chip discharge means adjacent the upper end of said vessel effective to maintain a predetermined level of the top of said mass of wood chips below the top of said vessel, strainer means in said vessel spaced a substantial distance below said wood chip discharge means for removal of treating liquid from said vessel, washing liquid inlet means in said vessel located a substantial distance above said strainer means for feeding washing liquid downwardly through a washing zone above said strainer means, a series of horizontal foraminous cylindrical drum washers of the type wherein washing liquid is sucked inwardly through the cylinder wall, means for separately collecting the filtrate from each washer, means for returning from the first washer at least a portion of the filtrate to the washing liquid inlet means in said vessel, and means for returning from each succeeding filter at least a portion of the filtrate to the preceding filter.

References Cited in the file of this patent UNITED STATES PATENTS 2,878,116 Carlsmith et al. Mar. 17, 1959 FOREIGN PATENTS 122,608 Sweden Aug. 31, 1948 

